An LSI such as an MPU (Microprocessor Unit), or the like, which operates at a high speed (at a high frequency), has a package structure of an LGA (Land Grid Array) type. In order to mount these LSIs on a mounting substrate such as a motherboard, or the like and to make these LSIs operate stably, the socket (the LGA socket) which is adaptable to the LGA package is needed.
In such LGA socket, as the conductive member for maintaining the mutual electrical connection between the LGA package and the motherboard, connection terminals (contact pins) are provided. For instance, the movable prove pin (also called the “pogo pin”) in which a spring is built, and the top end part is expanded and contracted vertically by the spring is employed. Also, the pin in which the top end part has the property of spring and is moved vertically, the pin (the spring terminal) in which the whole has the property of spring and is movable vertically, and the like are employed.
In the mode in which the pogo pin or the pin whose top end is shaped like a spring is used, through holes are formed in a heat resistant resin substrate, and then the pins are pushed into the through holes and mounted in it, and thus a resultant structure is used as the substrate for the LGA socket. On the other hand, in the mode in which the spring terminals are used, pins (spring terminals) are mounted on a printed substrate by the soldering, and thus a resultant structure is used as the substrate for the LGA socket.
An example of the mode in which the spring terminals are used is set forth in Patent Literature 1 (Japanese Laid-open Patent Publication No. 2010-277829).
When a transmission frequency of the signal is enhanced (a frequency of the signal is increased), the characteristic impedance of the transmission path is varied even though the signal transmission path has an infinitesimal length. For this reason, due to the mismatching of the characteristic impedance, a signal reflection is generated at the terminal of the transmission path, and then noise or phase shift of the signal is generated. As a result, the signal is not correctly transmitted, and thus it causes the occurrence of the malfunction in the circuit, or the like of the transmission destination.
As the countermeasure against these problems, in the signal wirings in the LSI or the LGA package and the signal wirings in the motherboard on which the LSI is mounted, the characteristic impedance is matched to 50Ω, and thus the signal reflection in the signal transmission path is suppressed.
On the contrary, in the wirings in the sockets which mutually connect the LGA package (LSI) and the motherboard, the impedance matching has not been particularly taken into account, under such an assumption that lengths of the wirings are almost negligible with respect to a transmission frequency of the signal (the wirings can be treated as lumped constant circuits).
However, a signal frequency of the LSI that includes a very high-speed arithmetic processing circuit such as MPU, or the like is reaching several GHz to several tens GHz. Therefore, also it is needed to treat the signal wirings in the sockets as distributed constant circuits to these frequencies. As a result, the signal wirings in the socket are now in such a situation that the signals cannot be correctly transmitted if the impedance matching is not properly applied to these signal wirings.
In the conventional socket which is adaptable to LGA package, the structure capable of matching and adjusting the impedances of the contact pins is not provided, in above both modes (the mode in which the pogo pins or the pins whose top end is shaped like a spring are employed, and the mode in which the spring terminals are employed). That is, the means for matching the impedances was not provided.